In order to improve safety of batteries, various studies have been conducted on batteries including a PTC element that prevents rapid temperature increase of batteries in case of short circuit.
For example, Japanese Patent Laid-Open No. 2003-217596 proposes that a surface of a negative current collector is coated with an electronic conductor mainly composed of polyethylene and having a PTC function. Japanese Patent Laid-Open No. 9-199106 proposes a lithium secondary battery in which a flange of a sealing plate peripheral edge is crimped via a gasket at an opening end of an external can, including a PTC element placed between the flange of the sealing plate and the gasket.
However, in Japanese Patent Laid-Open No. 2003-217596, the electronic conductor coated on the surface of the negative current collector is easily decomposed by an alkaline electrolyte, and the PTC function is sometimes insufficiently exerted.
In an alkaline battery, a negative current collector and a negative terminal plate need to be firmly connected by electric welding or the like, and it is difficult to integrate a PTC element between the negative current collector and the negative terminal plate.
The lithium secondary battery in Japanese Patent Laid-Open No. 9-199106 has a structure of a sealing portion such as a current collector or an explosion-proof mechanism different from a structure in an alkaline battery, and thus an assembling manner of the PTC element suitable for the structure of the alkaline battery needs to be considered.
Thus, in order to solve the conventional problems, the present invention has an object to provide an alkaline battery that is high in safety and reliability and highly resistant to liquid leakage.